1. Field of the Invention
This invention relates to entry system apparatus and more particularly to vacuum-to-vacuum entry system apparatus of the rotary type.
2. Description of the Prior Art
Entry systems and in particular vacuum entry systems of the rotary type are well known in the art, cf. for example, U.S. Pat. Nos. 3,260,383, 3,428,197, 3,833,018, and 3,931,789, to name just a few. Generally, a vacuum entry system is used in the placement of one or more workpieces into and/or out of an evacuated chamber as part of the fabrication or manufacturing process associated with the workpiece(s). During the passage of the workpiece(s), it is highly desirable that the integrity of the evacuated environment of the chamber be maintained.
For example, in the rotary type system of U.S. Pat. No. 3,260,383, this is accomplished by placing the workpiece in a recessed opening, which is at normal atmospheric pressure, of a rotatable member that is at a first angular position. The rotatable member is then rotated to a second position where the now workpiece loaded chamber is evacuated, i.e. depressurized, and next the member is rotated to a third position which aligns the now evacuated and workpiece loaded chamber with the opening of the main evacuated chamber in which the the workpiece is to be processed. Upon removal of the workpiece from the evacuated chamber of the rotating member into the main evacuated chamber, the member is then rotated back to the first position where the chamber is returned to normal atmospheric pressure and is ready to begin the next revolution and cycle with the next workpiece to be loaded therein. However, in this prior art system, mechanical seals in the form of rubber or plastic seal rings are used to seal off and isolate, the evacuated chamber of the rotating member, the main evacuated chamber, and the atmosphere with respect to one another. As a consequence, the friction created between the seals and the rotating member causes an increase in the torque requirements for the rotating member, as well as causing the seal interface to degrade and thus breakdown the seal between the evacuated chambers and/or atmosphere. Thus, this prior art system is not conducive to providing a vacuum entry system which is reliable and/or which has high throughput rates for processing the workpieces therein.
In U.S. Pat. No. 3,428,197, assigned to the common assignee herein, the rotary vacuum entry system thereof uses a pair of opposing flat plates, one of which is stationary and the other rotatable. The rotatable plate has three extended through openings that are equally radially and angularly spaced from the axis of rotation of the rotatable plate. Extended from the remote side of the rotatable plate are three article holding chambers each of which has a conformal opening which is in sealed and mounted abutment with one of the rotatable plate openings. The stationary member has an extended-through concentric arc-shaped slot through which the article in the holding chambers are passed into and out of the main evacuated chamber where the article is processed. The article is first loaded through another opening, i.e. the home opening, which is located on the remote side of the stationary member, this last mentioned opening being outside the main evacuated chamber and at atmospheric pressure. The home opening extends through the stationary member. In operation, the rotatable member is rotated to a position, i.e. the home position, that aligns one of its three openings with the home opening of the stationary member so that an article can pass through the aligned openings and into the article holding chamber. After the rotating member has been further rotated, it positions its particular opening associated with the now loaded article holding chamber with the aforementioned slot of the stationary member where it is passed from the article holding chamber into the main evacuated chamber for processing. Thereafter, the article is returned through the slot and back into the article handling chamber, and the rotatable member is rotated to the home position where the article is removed from the holding chamber through the aligned opening of the rotatable member and the home opening of the stationary member. An intermediate roughing pump stage position is provided between the home opening position and the workstation slot position. The system of U.S. Pat. No. 3,428,197 relies exclusively on the tight spacing between the opposing extremely flat surfaces of the members to prevent air leakage between the home, roughing and processing work stages. The stationary and rotatable members are maintained by a small separation of 0.00005 to 0.0010 inch by three equally spaced roller bearings that are mounted to and extend through the stationary plate so that their respective rollers contact the flat face of the rotatable member. As such, any eccentricity in one or more of the three bearings due to wear or variations in their manufacturing tolerances and/or variations in their vertical mounting positions and/or variations in the flatness of the plates will adversely affect the seal causing undesirable air leakage between the stages. Moreover, the system has additional torque requirements to overcome the rolling friction of the bearings against the rotatable member. As such, this prior art system is also not conducive to providing a vaccum entry system which is reliable and/or has high throughput rates for processing the workpieces therein.
The vacuum entry system of U.S. Pat. No. 3,833,018 is a rotary valve which uses a suction system to maintain a pressure differential in the clearance between the valve's cylindrical surface of the rotor and the compatibly contoured surface of the wall of the valve's rotor-receiving stationary chamber to control the air leakage between the high pressure side of the valve and its low pressure side. The actual clearance, however, is maintained independently by the mechanical supports that support the rotor or the shaft to which it is affixed. Thus, in this prior art system there is no way to compensate for variations in the concentricities of the rotor and/or curved chamber wall due to eccentricities in the rotor and/or wall and/or non-concentric alignment of the center axis of the chamber and that of the rotor. As a result, the system is conducive to degradation of the control of the air leakage making it unreliable and/or amenable to having a slow throughput rate. Moreover, because the control uses curved surfaces and the separation therebetween for its operation, the workpiece must pass through the rotor in a radial direction through an elongated slit or bore in the rotor. The slit lies in a predetermined diametral plane of the cylindrical rotor and is coincident with the axis of rotation. The article thus when passing through the slit is in a direction normal to and including the axis of rotation. As such, this prior art system cannot be used to process articles through a rotating member in a direction parallel to the axis of rotation, and/or offset from the axis of rotation, and is hence is not conducive to processing the articles at a high throughput rate.
The vacuum entry system of U.S. Pat. No. 3,931,789 uses sliding gate valves to enter and exit the articles thereof into the various vacuum chambers thereof. However, these type of prior art entry systems are also unsatisfactory. More particularly, during the periods that the value door is open, leakage occurs which compromises the integrity of the vacuum and/or increases the time to process the article because of the time needed to restore the integrity of the compromised vacuum. Moreover, slide valves have characteristically slow response times. Thus, the entry system of U.S. Pat. No. 3,931,789 is not reliable and/or isn't very conducive to high throughput because of its slow response time associated with such type valves and/or the aforementioned leakage and/or time needed to restore the integrity of the compromised vacuum.
In a non-vacuum entry system of the prior art, cf. U.S. Pat. No. 4,205,711, the automatic filling machine thereof, which is used for the dosing of powder from a hopper through an intermediate sector body to a rotatable dosing head, compressed air is used in the spacing between the concentric curved surfaces of the dosing drum head and the sector body to provide a hermetic seal for the opening of the body and the underlying powder carrying chambers of the rotating drum head. The hermetic seal provided by the compressed gas is only operative when the head is rotating, and, moreover, only during the rotation is the hermetic seal intended to prevent the powder from the opening of the body from entering the opening of the carrying chamber. During the rotational movement periods of the drum head, the sector body is in a retracted outward radial position with respect to the rotating head and is maintained at a spacing with respect to the head by a set of locator pins. During the periods of non-rotation of the head, the sector body is an extended radially inward position that places the body in contact with the head via another set of locator pins. The compressed gas is and must not be present during these last mentioned periods so as to allow the transfer, which is also in the radial direction, of the powder from the opening of the body to the aligned opening of one of the plural powder carrying chambers by suction means, which gas if otherwise present would prevent the transfer as explained previously. Thus, even though the compressed gas may also provide some lubrication between the moving parts, it is and can only be present during the actual rotation periods. Because of the intermittent presence of the gas and/or because of the requirement of curved surfaces for the sealing and/or lubrication operation, this prior art system is only useful for passing the powder through the aligned openings in a radial direction. In addition, the spacing between the two surfaces are maintained exclusively by independent mechanical means. Due to variations in the concentricity of the respective surfaces such as, for example, misalignment with respect to the axis of rotation, the seal is subject to leakage. Thus, this prior art entry system is not very reliable and/or has poor throughput rates. It is particularly not conducive for vacuum to vacuum entry systems and/or particularly for vacuum to vacuum entry systems of the rotary type in which the article passes through in a direction parallel to the axis and/or where the seal is required to be present as the transferring of the article from one vacuum to the other vacuum is taking place.
Moreover, as discussed in my aforementioned copending application, combination rotary gas bearing and sealing devices are well known in the art, cf. for example, U.S. Pat. Nos. 2,814,512, 3,733,490, 4,118,042, 4,191,385, and 4,361,332, to name just a few. In general, in such devices the gas of the bearing is used to effect the seal. However, heretofore in the prior art of which I am aware, the seal could only seal off a region of the bearing which encompassed the axis of rotation of the bearing, the seal and region being generally concentric with the axis. Thus, the prior art devices were not amenable to system apparatus in which there is a need to provide a seal for a region between two planar gas bearing surfaces of the bearing that is offset from the axis of rotation, i.e. a region which is radially offset from and doesn't include the axis of rotation. Hence, the prior art devices were not amenable to providing a seal for a low pressure region and especially a vacuumized opening in a rotary gas bearing using air or the like where the region has to be radially offset from and not encompass the bearing's axis of rotation.
In summary, none of the prior art of which I am aware contemplates a vacuum-to-vacuum entry system in combination with a combination rotary gas bearing and sealing device in the manner and according to the principles of the present invention as described herein.